Peptide multimeric contrast agents designed to bind to fibrin are described in Zhang, U.S. Pat. No. 7,238,341. Targeting peptides are described at the bottom of columns 35 and 36. However, binding to fibrin with conventional contrast agents developed in 2004 offers limited functionality.
In fact, currently the majority of imaging techniques offer limited functionality because they are invasive or have low spatial resolution. For example, conventional cancer imaging lacks target-specific contrast agents for accurate earlier diagnosis of malignant tumors. Furthermore, the results of the conventional cancer imaging are limited. MRI has improved spatial resolution that provides both anatomical and physiological information. However, MR images are only as useful as they are clear. Contrast agents are used to improve or increase the resolution of the image or to provide specific diagnostic information. Specifically, contrast agents detect cancer-related biomarkers and enhance the contrast of structures or fluids within the body in medical imaging.
To be effective, the contrast agent must interfere with the wavelength of electromagnetic radiation used in the imaging technique, alter the physical properties of tissue to yield an altered signal, or, as in the case of radiopharmaceuticals, provide the source of radiation itself. MRI and optical methods are unique among imaging modalities in that they yield complex signals that are sensitive to the chemical environment. While the signal from X-ray or radionuclide agents remains the same whether agents are free in plasma, bound to proteins or other targets, or trapped inside bone, certain contrast agents for MRI and optical imaging will have different signal characteristics in differing physiological environments. If the contrast agent is not sufficiently sensitive or present at high enough concentration, the signal changes may not be observed. If the signal changes are not observed the resulting MR images will be inaccurate or misleading, which may result in a misdiagnosis.